The present invention relates in general terms to furnaces for producing or melting oxide materials, such as glass or ceramics, which have walls cooled by a flow of water.
The present invention more specifically relates to the problem of drawing off material melted in the furnace or melter and for this purpose aims at improving the prior art solutions which will now be described with reference to FIGS. 1a, 1b and 1c.
In these drawings the reference 2 designates the walls of a melting furnace or melter filled with a glass or a ceramic material in the liquid state 4.
FIG. 1a illustrates the simple, well-known process of sampling by over-flow, in which the side walls of the melter have an unequal height and by means of a throat 6 permit the discharge of the melted material by overflowing from part of the melter wall.
FIGS. 1b and 1c illustrate known solutions for sampling by extraction by gravity from an orifice made in the lower walls of the melter. In the case of FIG. 1b, direct sampling in the floor of the melter takes place by a pipe 8, heated by a lateral electric furnace 10, able to maintain the material in the molten state during its extraction. A thermal glass plug 12 obtained through the cooling of the pouring tube then makes it possible to seal the orifice when the necessary molten material quantity has been extracted.
FIG. 1c shows the same elements as in FIG. 1b, but with a metal plug 14 cooled by a flow of water in an envelope surrounding it and which is brought to the sampling orifice in order to seal the latter by cooling.
In the examples of FIGS. 1b and 1c, the pouring tubes are made from refractory material or precious metals, such as molybdenum and platinum, being reheated by an auxiliary, resistance or induction furnace 10.
The start of pouring or casting is controlled by adapting the internal diameter of the orifice, the length of the pouring tube and its temperature to the hydrodynamic characteristics of the molten material (viscosity).
A description of these procedures appear in the documentation of the Vienna Conference of IAEA, September 1986, in the article entitled "GLASS-MELTER MATERIALS: TECHNICAL OPTIONS FOR THE FRENCH VITRIFICATION PROCESS AND OPERATIONS EXPERIENCE AUTHORS", by R. BONNIAUD (CEA IRDI, Marcoule), R. DEMAY (CEA, IRDI, Fontenay-aux-Roses), R. RICHTER (SGN, St. Quentin en Yvelines) and L. ROZAND (COGEMA, St. Quentin en Yvelines).
However, these devices suffer from a certain number of deficiencies, which can be accepted in the glassmaking industry:
the refractory parts are consumable wear-prone parts, PA1 the pouring stopping plugs interposed in the glass jet lead to liquid glass splashing, PA1 the cooling of the pouring tubes in order to set a glass plug takes place with a very considerable inertia and the operation is impossible when the glass flows at a temperature well above its softening point and when the melter is filled with molten glass. PA1 in the floor of the melter, an orifice whose diameter D is equal to or larger than the thickness H of the wall forming the melter, PA1 a metal sleeve, whose base has a shoulder which can be adapted to the side walls of the orifice, said sleeve having a central passage forming the pouring tube for the molten material, a clearance being provided between the side walls of the orifice and the base of the sleeve in order to receive an insulating material between said sleeve and the cold floor of the melter, PA1 beneath the floor of the melter a device having a cooled, sliding blade, equipped with an actuator controlling its movement in translation along the orifice, thus determining its more or less large opening or closing state.
However, these deficiencies are unacceptable in the case of cold structure, direct induction furnaces. Thus, in these furnaces, where the walls and floor are entirely cooled have no refractory material parts and therefore has a very considerable service life. This type of furnace is generally small with a reduced molten glass mass and the pouring device must permit a rapid action on the drawing off of the glass.
For an application in a nuclear environment, where this type of furnace is particularly suitable, the glass pouring stoppages must be very specific and must not splash molten glass onto the installations.